Gas turbine fan casing having a belt for fastening equipment

ABSTRACT

The invention relates to a gas turbine fan casing ( 10 ) comprising an annular casing wall ( 12 ) centered on a longitudinal axis (X-X) of the casing and at least one fastening belt ( 100 ) mounted on the periphery of the casing wall to fasten equipment on the casing, each fastening belt comprising two distinct annular flanges ( 102, 104 ) each having an L-shaped straight section, said flanges being fastened to each other and maintained on the wall of the casing by tightening of the inverted cone type.

BACKGROUND OF THE INVENTION

The present invention relates to the general field of gas turbine casings, and more particularly gas turbine fan casings for aeronautic engines.

In a gas turbine aeronautic engine, the casing is made up of a part forming an air intake sleeve, the function of which is to define the air intake tunnel in the engine, and a part forming the fan casing.

The fan casing in particular serves to retain debris, such as ingested objects or damaged blade fragments, projected by centrifugation, so as to prevent them from passing through the casing and reaching other parts of the aircraft. The fan casing also supports a certain number of pieces of equipment or compartments of the engine, for example such as the hoses conveying deicing fluid or the logic controller of the engine.

Commonly, a fan casing is made up of a metal wall defining the intake tunnel. Between the ends of said wall, circumferential structural reinforcing webs are added, said webs also being able to serve to support equipment of the engine.

Furthermore, it has been proposed to make the fan casing from a composite material of the fiber/resin type through the production of a fibrous preform, impregnation with a resin, and molding to obtain a desired shape directly. In fact, compared to metal, the composite makes it possible to obtain significant mass savings.

However, the use of the composite material to produce a fan casing poses the problem of fastening the equipment of the engine on the casing. In particular, the solution consisting of gluing annular flanges on the wall of the casing to fasten the equipment thereto is not fully satisfactory. In fact, the certification of the gluing of parts that perform a structural function (namely the fastening flanges) is extremely complex to obtain. Likewise, the solution consisting of bolting the fastening flanges on the wall of the casing is not satisfactory, since it requires piercing the composite structure of the casing with all of the drawbacks that that entails (discontinuity of the fibers, weakening of the structure, concentration of stresses at the piercings, etc.).

Also known from document WO 2009/147307 is a solution consisting of attaching a belt forming a gripping collar gripping the casing on the outer periphery of the casing. This solution does not have the aforementioned drawbacks. However, this principle of fastening by strapping requires a closing point for the belt which, in case of breakage, leaves the belt free with all of the ensuing consequences.

SUBJECT-MATTER AND BRIEF DESCRIPTION OF THE INVENTION

The present invention therefore primarily aims to obviate such drawbacks by proposing a solution for fastening equipment on a fan casing, in particular made from a composite material, that does not require gluing, piercing or using single fastening points.

This aim is achieved owing to a gas turbine fan casing comprising an annular casing wall centered on a longitudinal axis of the casing and at least one fastening belt mounted on the periphery of the casing wall to fasten equipment on the casing, and wherein, according to the invention, each fastening belt comprises two distinct annular flanges each having an L-shaped straight section, said flanges being fastened to each other and maintained on the wall of the casing by tightening of the inverted cone type.

The fastening belt is mounted on the casing wall by tightening of the inverted cone type. This type of tightening consists of strapping the belt on the casing by conical rubbing of its flanges on the casing wall. Thus, the maintenance of the belt on the casing wall is done without using gluing or piercing of the wall of the casing. Likewise, the belt can completely cover the circumference of the casing wall without needing to use a single closing point of the belt, which avoids the problems related to the rupture of such a point. Lastly, the maintenance of such a fastening belt is facilitated as a result.

Preferably, the two flanges of a same fastening belt are maintained by tightening on a crown of the wall of the casing having two opposite planes that are inclined relative to the longitudinal axis of the casing.

Also preferably, each flange of a same fastening belt has a contact leg bearing on one of the inclined planes of the crown and a tightening leg designed to be assembled to the tightening leg of the other flange of said belt.

The planes of the crown may be inclined in an open cone toward the inside of the wall of the casing, the casing further comprising tightening means to assemble the tightening legs of two flanges of the fastening belt to each other by bringing them closer to each other so as to ensure tightening thereof on the wall of the casing.

Alternatively, the planes of the crown may be inclined in an open cone toward the outside of the wall of the casing, the casing further comprising tightening means to assemble the tightening legs of the two flanges of the fastening belt to each other by separating them from one another so as to ensure tightening thereof on the wall of the casing.

The tightening means of these two embodiments may comprise screw/nut systems.

The casing may comprise a plurality of fastening belts axially spaced apart from each other. At least some of these fastening belts can be assembled to each other to form an extremely high-performance fastening element (this element may for example serve to ensure fastening of the engine on the wing of the aircraft).

Also preferably, the casing wall is made from composite material with a fibrous reinforcement densified by a matrix.

The invention also relates to an aeronautic gas turbine engine having a fan casing as previously defined.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will emerge from the description provided below, in reference to the appended drawings which illustrate one non-limiting example embodiment thereof. In the figures:

FIG. 1 is a very diagrammatic view of an aeronautic engine gas turbine;

FIG. 2 is a partial axial cross-sectional view showing a fastening belt assembled on the fan casing for a gas turbine like that of FIG. 1;

FIG. 3 is an enlarged and exploded view of the fastening belt of FIG. 2;

FIG. 4 is a view of a fastening belt for a fan casing according to another embodiment of the invention; and

FIG. 5 illustrates still another embodiment of the fan casing according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be described hereafter in the context of its application to the manufacture of a fan casing for an aeronautic engine with a gas turbine.

Such an engine, as very diagrammatically shown in FIG. 1, comprises, from upstream to downstream in the gas flow direction, a fan 1 positioned at the input of the engine, a compressor 2, a combustion chamber 3, a high-pressure (HP) turbine 4 and a low-pressure (LP) turbine 5. The HP and LP turbines are respectively coupled to the compressor and the fan by respective coaxial shafts and are centered on a longitudinal axis X-X of the engine.

The engine is housed inside a casing comprising several parts corresponding to different elements of the engine. Thus, the fan 1 is surrounded by a fan casing 10.

FIG. 2 shows a fan casing profile 10 made from a composite material according to one embodiment of the invention. The casing 10 comprises an annular wall 12 centered on the longitudinal axis X-X of the engine and whereof the inner surface 12 a defines the air intake tunnel. The latter may be provided with an abradable coating layer (not shown) at the trajectory of the blade apices of the fan, a plate 14 being partially shown very diagrammatically. An acoustic treatment coating (not shown) may furthermore be positioned on the inner surface of the casing, in particular upstream from the abradable coating.

The casing 10 may be provided with outer flanges 16, 18 at the upstream and downstream ends of the annular wall 12 so as to allow it to be mounted and connected with other elements.

Preferably, the casing 10 is made from a composite material with a fibrous reinforcement densified by a matrix. The reinforcement is for example made from carbon, glass, aramid or ceramic fibers, and the matrix from polymer, for example epoxide, bismaleimide or polyimide.

To that end, as indicated in document EP 1,961,923, the fibrous reinforcement may be formed by winding a fibrous texture made by three-dimensional weaving on a mandrel, the mandrel having a profile corresponding to that of the casing to be produced.

Advantageously, the fibrous reinforcement constitutes a complete tubular fibrous preform of the casing 10 forming a single piece with a corresponding part of the annular wall and the reinforcing parts corresponding to the outer flanges 16, 18.

The fan casing 10 also comprises at least one fastening belt 100, 100′ that is mounted on the periphery of the casing wall 12 so as to allow the equipment to be fastened on the casing.

According to the invention, each fastening belt 100, 100′ comprises two distinct annular flanges 102, 104 each having an L-shaped straight section, said flanges being in opposition, fixed to one another and maintained on the wall 12 of the casing 10 by tightening of the inverted cone type. In the embodiment of FIGS. 2 and 3, the flanges 102, 104 are 360° parts.

The two flanges 102, 104 of a same fastening belt 100, 100′ are more specifically maintained by tightening on a crown 106 of the wall 12 of the casing, said crown 106 having two opposite planes 108, 110 that are inclined relative to the longitudinal axis X-X of the engine.

Thus, in the embodiment of FIGS. 2 and 3, the planes 108, 110 of the crown 106 are inclined so as to form a cone that is open toward the inside of the wall of the casing. In longitudinal cross-section, the crown 106 has a triangular shape whereof the apex is oriented toward the outside of the casing.

Alternatively, in the embodiment of FIG. 4, the planes 108′, 110′ of the crown 106′ are inclined so as to form a cone that is open toward the outside of the wall of the casing. In longitudinal cross-section, the crown 106′ thus has a triangular shape whereof the apex is oriented toward the inside of the casing.

Furthermore, each flange 102, 106 of a same fastening belt 100 has a contact leg 102 a, 104 a, respectively, that bears on one of the inclined planes of the crown 106, 106′ and a tightening leg 102 b, 104 b, respectively, which is designed to be assembled to the tightening leg of the other flange of the fastening belt by tightening means described later.

Furthermore, in light of the particular shape of the crown 106 of the embodiment of FIGS. 2 and 3, for each flange 102, 104 of a same tightening belt, the contact and tightening legs form an angle a of more than 90° between them. Likewise, due to the particular shape of the crown 106′ of the embodiment of FIG. 4, the contact and tightening legs of the flanges 102, 104 of a same fastening belt of this embodiment form an angle β of less than 90° between them.

The casing further comprises tightening means for assembling the tightening legs 102 b, 104 b of the two flanges 102, 104 of the fastening belt 100, 100′ to each other.

In the embodiment of FIGS. 2 and 3, these tightening means assume the form of screws 112 on which nuts 114 are tightened, the screws passing through the tightening legs 102 b, 104 b of the two flanges 102, 104 in a direction substantially parallel to the longitudinal axis X-X of the engine.

In this way, by tightening the nuts 114 against the tightening legs 102, 104 b of the two flanges, the latter will tend to come closer to each other and “rise” on the respective inclined planes 108, 110 of the crown 106 so as to ensure tightening of the fastening belt 100 on the wall 12 of the casing.

In the embodiment of FIG. 4, the tightening means also assume the form of screws 112 on which nuts 114 are tightened, the screws passing through the tightening legs 102 b, 104 b of the two flanges 102, 104 in a direction substantially parallel to the longitudinal axis X-X.

The tightening means also comprise spring washers 116 that are inserted between the tightening legs 102 b, 104 b of the two flanges 102, 104. In this way, by tightening the nuts 114 against the tightening legs 102, 104 b of the two flanges, the latter will tend to move away from each other (under the effect of the spring washers 116) and to “rise” on the respective inclined planes 108′, 110′ of the crown 106′ so as to ensure tightening of the fasting belt 100 on the wall 12 of the casing.

It will be noted that the screws 112 used to tighten the fastening belt on the wall of the casing may also serve to fasten elements 118 of the pieces of equipment or engine compartments of the engine.

The mounting of the fastening belt 100 of the embodiment of FIGS. 2 and 3 is done as follows. The flanges thereof are brought around the casing wall (the flange 102 from downstream and the flange 104 from upstream) and moved axially toward one another (casing of FIG. 3). The screws 112 are then inserted into their respective tightening legs and the nuts 114 are tightened against the latter to ensure maintenance of the fastening belt on the casing.

For mounting of the fastening belt 100′ of the embodiment of FIG. 4, it is necessary for the two flanges 102, 104 each to be made in two parts. For example, it is possible to consider that the two parts of the same flange are assembled around the casing wall with a bevel-shaped partial angular overlap.

A description will be provided of another embodiment of a fan casing according to the invention with respect to FIG. 5.

In this embodiment, it is provided that the fan casing 10 bears three fastening bolts 100 axially spaced apart from each other and connected to each other by their respective screws 112. More specifically, the screws 112 serving to tighten the fastening bolts 100 on the wall 12 of the casing are the same for all three belts.

Such an assembly of several fastening belts to each other makes it possible to form an extremely powerful fastening element, the latter for example being able to serve to ensure fastening of the engine on the wing of the aircraft.

We will now describe certain features shared by all of the embodiments previously described.

The crowns 106, 106′ on which the flanges of the fastening belts 100, 100′ are mounted can be obtained by locally varying the thickness of the wall 12 of the casing during the manufacture thereof. Thus, this overthickness may be obtained either by using threads with a larger size at the overthickness to be created during the weaving of the fibrous texture wound on the mandrel, or by introducing an insert between the different layers of fibrous texture wound on the mandrel. In the event the wall of the casing is manufactured by stratification, the necessary overthickness will be obtained by performing different windings.

It is possible to decrease the height of the flanges 102, 104 (or specifically the respective tightening legs 102 b, 104 b) locally in the areas in which no fastening of equipment or engine compartments of the engine is provided. Mass savings may thus be expected.

The contact dimension between the contact legs 102 a, 104 a of the flanges 102, 104 of the fastening belts and the inclined planes of the crowns 106, 106′ of the casing wall may vary between 1 mm and several centimeters. However, in the case where the flanges are made from a different material from that of the casing wall, it will be necessary to be careful to account for the expansion differences between these materials in particular to prevent an increase in the diameter due to expansion of the flanges from causing sliding on the crown. 

1. A gas turbine fan casing comprising an annular casing wall centered on a longitudinal axis of the casing and at least one fastening belt mounted on a periphery of the casing wall to fasten equipment on the casing, and wherein, each fastening belt comprises two distinct annular flanges each having an L-shaped straight section, said flanges being fastened to each other and maintained on the wall of the casing by an inverted cone tightening mechanism.
 2. The casing according to claim 1, wherein two flanges of a same fastening belt are maintained by tightening on a crown of the wall of the casing having two opposite planes that are inclined relative to the longitudinal axis of the casing.
 3. The casing according to claim 2, wherein each flange of a same fastening belt has a contact leg bearing on one of the inclined planes of the crown and a tightening leg designed to be assembled to the tightening leg of the other flange of said belt.
 4. The casing according to claim 3, wherein the planes of the crown are inclined in an open cone toward an inside of the wall of the casing, the casing further comprising tightening devices to assemble the tightening legs of two flanges of the fastening belt to each other by bringing said tightening legs closer to each other so as to ensure tightening thereof on the wall of the casing.
 5. The casing according to claim 3, wherein the planes of the crown are inclined in an open cone toward the outside of the wall of the casing, the casing further comprising tightening devices to assemble the tightening legs of the two flanges of the fastening belt to each other by separating them from one another so as to ensure tightening thereof on the wall of the casing.
 6. The casing according to claim 4, wherein the tightening devices comprise screw/nut systems.
 7. The casing according to claim 1, comprising a plurality of fastening belts axially spaced apart from each other.
 8. The casing according to claim 7, wherein at least some of the fastening belts are assembled to each other.
 9. The casing according to claim 1, wherein the casing wall is made from composite material with a fibrous reinforcement densified by a matrix.
 10. An aeronautic gas turbine engine having a fan casing according to claim
 1. 